Can a carrier reject a damage claim because the outer packaging was insufficient?

Yes. Under standard European carrier terms, a damage claim is rejected or reduced when the carrier determines at delivery that the outer packaging was inadequate for the declared weight or the fragility of the contents. The baseline conditions for a covered claim are: double-wall cardboard above 20 kg, void fill against movement, and fragile marking on all four vertical faces. A package arriving damaged inside sound outer packaging is a carrier handling issue. A package arriving damaged inside a crushed single-wall box at 25 kg is a packaging issue.